PROJECT SUMMARY RELEVANCE: About 1/3 of adults and 1/5 of children and adolescents in the U.S. are obese, with socially disadvantaged individuals being disproportionately affected. Rapid, excessive weight gain in early life often translates into persistent obesity, which may be in turn be associated with earlier onset of several health complications. Differences in obesity timing thus may be a vital way in which race-ethnic, socioeconomic and regional disparities in health widen over the life course. OBJECTIVES: Our study will measure the dynamics of weight status during childhood, adolescence, and young adulthood and link these dynamics with subsequent health outcomes. A key contribution of our study is the careful and judicious use of statistical techniques to combine existing high-quality national longitudinal cohorts into a synthetic cohort of over 90,0000, followed from birth to age 55, reflective of recent experiences. AIMS: 1) Estimate the overall and sub-population dynamics of obesity, including the age and timing of obesity onset, age-specific incidence, obesity duration and intensity, weight fluctuations, and cumulative exposure to unhealthy weight. 2) Calculate the sub-population cumulative exposure to high BMI during childhood, adolescence and young adulthood for contemporary U.S. cohorts. 3) Estimate individual associations between exposure to high BMI across the first decades of life and adult health, specifically diabetes, cardiovascular, metabolic, and gastrointestinal diseases and quality of life, to quantify the health effects of early-life obesity dynamics. 4) Estimate the contribution of disparities in obesity dynamics early in life to disparities in other health outcomes across race-ethnic, SES, and urbanicity groups. 5) Develop a simulation to model the effects of interventions to reduce childhood obesity on national burdens of adult disease and disparities in disease. DESIGN: We will integrate 7 datasets into a single nationally- representative synthetic cohort. We will use recently-tested approaches to model multiple dimensions of weight dynamics. We will estimate the average number of years spent obese, as well as a continuous measure of BMI-years. We will link an individual?s obesity history with health complications using additive, duration, peak BMI, and weight change models. We will evaluate obesity dynamics separately in underserved race-ethnic, SES, and rural populations and will use decomposition approaches to quantify the contributions of these dynamic to disparities in health conditions. We will develop a ?macro-simulation? that allows us to assess the impact of reductions in obesity incidence at key points in childhood and adolescence on the national prevalence of obesity in adulthood, health complications in adulthood, and race, ethnic, socioeconomic and urbanicity disparities in obesity and other chronic conditions. SIGNIFICANCE: The creation of a synthetic national cohort addresses the critical absence of nationally representative data to track obesity from childhood into adulthood. Our research will provide the first comprehensive set of estimates of exposure to obesity during the first decades of life and their contribution to health and disparities in health over the lifespan.